110 ANNUAL OF SCIENTIFIC DISCOVERY. 



much more accurately than it could be by any other method. But in 

 determining the longitude, it becomes a matter of importance to ascer- 

 tain whether the current does really pass over the wires in a time im- 

 measurably small, as has been commonly stated. The longitude, it 

 is well known, is determined by the difference in the time of the 

 transit of any star at the two places, and as soon as it is observed at 

 one place, the observer, by touching a key, records the fact at the 

 other, by means of an astronomical clock ; bnt if any measurable time 

 is consumed in the passage of the current which causes this record, it 

 must be taken into the account. This subject first attracted the at- 

 tention of Mr. Walker, of Washington, while ascertaining the longi- 

 tudes of Cambridge and Philadelphia, and he then became convinced 

 that the time required by the galvanic stream is by no means immeas- 

 urably small, but can be determined, and amounts, between Cam- 

 bridge and Philadelphia, to nearly one twentieth of a second, being, 

 therefore, very much greater than would have been expected from 

 analogy, after Wheatstone's measurement of the velocity of propaga- 

 tion for friction-electricity. Mr. Walker deduces this value from all 

 the comparisons which were made between the three stations, Cam- 

 bridge, Philadelphia, and New York, and thus finds from 18 equations 

 of condition, that the galvanic current would traverse 18,700 miles in 

 a second. This value is determined to within about 1,000 miles, 



or / 8 . 



This beautiful result is, in its scientific relations, the more interest- 

 ing from the fact that the galvanic current here traverses different 

 mediums, the conducting wire (iron), three batteries, and the 

 earth, a total length of 1,050 miles. It is particularly striking that 

 the velocity of the galvanic current is so much less than that of fric- 

 tion-electricity, according to Wheatstone's observations. 



Having formed this opinion, Mr. Walker, of course, felt anxious to 

 verify it, and for this purpose has been engaged in some experiments 

 between Washington and Cincinnati, which are described by Professor 

 Mitchell, in a recent letter. He says, "The principle employed is 

 very simple, and may be easily understood by those not familiar with 

 the subject. Suppose it possible to start two clocks to beating at the 

 same absolute moment of time in Washington and Cincinnati, and that 

 these beats are both recorded at each station. The Cincinnati clock- 

 beat recorded in Cincinnati by a current of electricity having no distance 

 to go is done instantly, while the Washington clock-beat, being re- 

 corded by a current corning from Washington (in case this current 

 should require, say, one tenth of a second of time to pass from Wash- 

 ington to Cincinnati), will fall behind the Cincinnati clock-beat, on 

 the record, by that time, or by one tenth of a second. The reverse is 

 true on the record in Washington. There it is manifest that the 

 Washington clock-beat precedes the Cincinnati clock-beat, in case 

 there be wave-time, and a comparison of the two records (in case no 

 modifying circumstances come in) would show the wave-time, should 

 any exist." 



In a recent article in the Astronomical Journal, Professor Mitchell 

 gives a detailed account of some of his experiments with reference to 



